1. Field of the Invention
This invention relates to implantable devices and more particularly relates to the design and manufacture of implantable leads.
2. Description of the Related Art
An increasingly popular technique for therapeutically treating neurological disorders and chronic pain is providing electrical stimulation to neural tissue within the brain, the spinal cord, and/or a peripheral nerve. Thus, for example, physicians may surgically implant leads having electrode contacts near the spinal column of the human body and deliver electrical energy, using a signal generator, to these contacts to stimulate targeted neural tissue and elicit the desired therapeutic relief.
Implantable leads now also provide electrical stimulation via more than one electrode. This significantly increases the functionality of the implantable lead. For example, a multiple electrode lead allows the physician to adjust the treatment therapy to target different neural tissue, or to direct the stimulation more precisely to the neural tissue of interest. This is particularly useful where the implanted lead migrates along the spinal cord after it has been implanted. By subsequently adjusting the electrical stimulation delivered by the multi-electrode lead, the need for a second surgery is avoided.
A commonly-used implantable lead is a Pisces-style lead. As depicted in FIGS. 1A and 1B, this lead is a long and narrow tube, typically polyurethane, having an outside diameter of 0.050xe2x80x3 and an inside diameter of 0.030xe2x80x3. Along the distal end 120 of the lead are one or more electrodes 105 that wrap around the circumference of the lead body and have a certain width. These electrodes 105 are coupled to respective wires 110 that run from within a lumen 117 of the lead tubing to corresponding connectors 115 along the proximal end 125 of the lead. Most implantable leads utilized today are based on a coiled-spring design. In such leads, the wires that are used to connect the lead to the electrodes are wrapped around a mandrel with enough tension to cause the wires to exceed their yield point and thus to hold a coiled shape. The coiled wires are insulated from each other and typically have a fixed pitch, namely a fixed number of revolutions per inch. Each coiled wire is coupled to a corresponding electrode along the lead body. This is achieved by having the distal end of the wire (the filar) exit tangentially from the coil along the distal end of the lead and then be connected to an electrode located at that portion of the lead.
The coiled-spring design of the implantable leads, however, is limiting in its difficulty of assembly with the electrodes. In particular, the coiled-spring wires are unwound along the distal end of the lead and extended tangentially from the coil at along the desired portion of the lead where the corresponding electrode for each wire is to be placed. The tangentially extending wires are typically referred to as filars. This unwinding process, however, is inaccurate resulting in the filars extending unevenly from the coil. This results in non-coplanar weld placement of the electrode contacts over the filars.
After placement of the electrodes, the filars are positioned and trimmed while maintaining contact with the corresponding electrodes. A filar for the wire corresponding to an electrode is placed within a slot of the electrode and put in contact with that electrode and welded. The resulting weld, however, often protrudes from the surface of the lead, potentially causing interference during implant.
Further inefficiencies result in the overall manufacture of the Pisces-style lead. Known procedures for manufacturing implantable leads require considerable steps and operator involvement. Multiple cure processes must be performed requiring as much as 2-3 days of cure time. The greater the number of leads, the greater time and cost required in manufacturing the lead. Further, manufacture of these leads requires skilled technicians to perform some of these manufacturing steps.
It is therefore desirable to provide a design for and a method of manufacture of an implantable lead that can overcome these and other disadvantages.
A preferred form of the invention is an implantable lead and a method of manufacture of the lead. The implantable lead has flexible tubing impressions, contact sleeves positioned over the impressions and having openings, and a wire coil member running along a central lumen portion of the lead. The wire coil has radially extending filars that extend in a substantially perpendicular axis relative to the surface of the wire coil. Further, the wire coil has fixed and variable pitch portions to provide accurate positioning of the radially extending filars.
The method of manufacture includes the steps of forming a coil having at least one wire member having fixed and variable pitches, each wire member having a filar member, extending the filar member of at least one of the wire members radially from the coil member at a predetermined portion along the variable pitch portion of the coil member, heat forming a flexible lead body over the coil member, providing a contact sleeve over a portion of the lead body, the contact sleeve having a opening for receipt of the filar member, and welding the filar member to the contact sleeve.
The design and process of the implantable lead of the present invention provides a number of advantages over leads of the prior art. By way of examples, the present invention provides a wire coil design that provides improved accuracy in distances between the filars and improved assembly with the electrodes. In addition, the present invention reduces the direct build time of the lead, reduces the required level of operator training to manufacture the lead, and requires less manufacturing floor space. The applicant estimates that each of these variables may be reduced by as much as 50% over prior art techniques.